<!DOCTYPE html>
<html>
<head>
    
<!-- Google Analytics -->
<script>
window.ga=window.ga||function(){(ga.q=ga.q||[]).push(arguments)};ga.l=+new Date;
ga('create', 'UA-104674648-1', 'auto');
ga('send', 'pageview');
</script>
<script async src='https://www.google-analytics.com/analytics.js'></script>
<!-- End Google Analytics -->


    

    
<!-- Baidu Tongji -->
<script>var _hmt = _hmt || []</script>
<script async src="//hm.baidu.com/hm.js?d230cbd4c1f4abd065bc1ca0e61663da"></script>
<!-- End Baidu Tongji -->




    <meta charset="utf-8">
    
    <meta name="google-site-verification" content="x0NhT11Wdmfn9lsdbcQQOIhQHQKeNWATVfTj5rYZWXo">
    
    
    
    
    <title>通信原理学习记录（一） | Zhuhao&#39;s Blog | I am the captain of my ship and the master of my fate.</title>
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
    
    <meta name="theme-color" content="#3F51B5">
    
    
    <meta name="keywords" content="wireless">
    <meta name="description" content="通信原理学习记录（一） 今天刚刚开始学习通信原理，了解了通信原理的知识点，大概是要学习模拟通信与数字通信，模拟通信技术在之前的高频学习中已经有了一定的基础了，对一些调制技术有了一定的认识和分析能力，因此，本学习的通信原理主要的难度在于数字通信技术。">
<meta name="keywords" content="wireless">
<meta property="og:type" content="article">
<meta property="og:title" content="通信原理学习记录（一）">
<meta property="og:url" content="http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/index.html">
<meta property="og:site_name" content="Zhuhao&#39;s Blog">
<meta property="og:description" content="通信原理学习记录（一） 今天刚刚开始学习通信原理，了解了通信原理的知识点，大概是要学习模拟通信与数字通信，模拟通信技术在之前的高频学习中已经有了一定的基础了，对一些调制技术有了一定的认识和分析能力，因此，本学习的通信原理主要的难度在于数字通信技术。">
<meta property="og:locale" content="zh-CN">
<meta property="og:image" content="http://greedyhao.cc/img/wireless/wireless_overview.png">
<meta property="og:image" content="http://greedyhao.cc/img/wechat_official_accounts.jpg">
<meta property="og:updated_time" content="2018-09-09T05:52:39.288Z">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="通信原理学习记录（一）">
<meta name="twitter:description" content="通信原理学习记录（一） 今天刚刚开始学习通信原理，了解了通信原理的知识点，大概是要学习模拟通信与数字通信，模拟通信技术在之前的高频学习中已经有了一定的基础了，对一些调制技术有了一定的认识和分析能力，因此，本学习的通信原理主要的难度在于数字通信技术。">
<meta name="twitter:image" content="http://greedyhao.cc/img/wireless/wireless_overview.png">
    
        <link rel="alternate" type="application/atom+xml" title="Zhuhao&#39;s Blog" href="/atom.xml">
    
    <link rel="shortcut icon" href="/favicon.png">
    <link rel="stylesheet" href="//unpkg.com/hexo-theme-material-indigo@latest/css/style.css">
    <script>window.lazyScripts=[]</script>

    <!-- custom head -->
    

</head>

<body>
    <div id="loading" class="active"></div>

    <aside id="menu" class="hide" >
  <div class="inner flex-row-vertical">
    <a href="javascript:;" class="header-icon waves-effect waves-circle waves-light" id="menu-off">
        <i class="icon icon-lg icon-close"></i>
    </a>
    <div class="brand-wrap" style="background-image:url(/img/brand.jpg)">
      <div class="brand">
        <a href="/" class="avatar waves-effect waves-circle waves-light">
          <img src="/img/portrait.jpg">
        </a>
        <hgroup class="introduce">
          <h5 class="nickname">Greedyhao</h5>
          <a href="mailto:hao_kr@163.com" title="hao_kr@163.com" class="mail">hao_kr@163.com</a>
        </hgroup>
      </div>
    </div>
    <div class="scroll-wrap flex-col">
      <ul class="nav">
        
            <li class="waves-block waves-effect">
              <a href="/"  >
                <i class="icon icon-lg icon-home"></i>
                主页
              </a>
            </li>
        
            <li class="waves-block waves-effect">
              <a href="/archives"  >
                <i class="icon icon-lg icon-archives"></i>
                Archives
              </a>
            </li>
        
            <li class="waves-block waves-effect">
              <a href="/tags"  >
                <i class="icon icon-lg icon-tags"></i>
                Tags
              </a>
            </li>
        
            <li class="waves-block waves-effect">
              <a href="/categories"  >
                <i class="icon icon-lg icon-th-list"></i>
                Categories
              </a>
            </li>
        
            <li class="waves-block waves-effect">
              <a href="https://github.com/greedyhao" target="_blank" >
                <i class="icon icon-lg icon-github"></i>
                Github
              </a>
            </li>
        
      </ul>
    </div>
  </div>
</aside>

    <main id="main">
        <header class="top-header" id="header">
    <div class="flex-row">
        <a href="javascript:;" class="header-icon waves-effect waves-circle waves-light on" id="menu-toggle">
          <i class="icon icon-lg icon-navicon"></i>
        </a>
        <div class="flex-col header-title ellipsis">通信原理学习记录（一）</div>
        
        <div class="search-wrap" id="search-wrap">
            <a href="javascript:;" class="header-icon waves-effect waves-circle waves-light" id="back">
                <i class="icon icon-lg icon-chevron-left"></i>
            </a>
            <input type="text" id="key" class="search-input" autocomplete="off" placeholder="输入感兴趣的关键字">
            <a href="javascript:;" class="header-icon waves-effect waves-circle waves-light" id="search">
                <i class="icon icon-lg icon-search"></i>
            </a>
        </div>
        
        
        <a href="javascript:;" class="header-icon waves-effect waves-circle waves-light" id="menuShare">
            <i class="icon icon-lg icon-share-alt"></i>
        </a>
        
    </div>
</header>
<header class="content-header post-header">

    <div class="container fade-scale">
        <h1 class="title">通信原理学习记录（一）</h1>
        <h5 class="subtitle">
            
                <time datetime="2018-08-08T09:34:52.000Z" itemprop="datePublished" class="page-time">
  2018-08-08
</time>


	<ul class="article-category-list"><li class="article-category-list-item"><a class="article-category-list-link" href="/categories/工作/">工作</a></li></ul>

            
        </h5>
    </div>

    


</header>


<div class="container body-wrap">
    
    <aside class="post-widget">
        <nav class="post-toc-wrap post-toc-shrink" id="post-toc">
            <h4>TOC</h4>
            <ol class="post-toc"><li class="post-toc-item post-toc-level-1"><a class="post-toc-link" href="#通信原理学习记录一"><span class="post-toc-number">1.</span> <span class="post-toc-text">通信原理学习记录（一）</span></a></li><li class="post-toc-item post-toc-level-1"><a class="post-toc-link" href="#信息及其度量"><span class="post-toc-number">2.</span> <span class="post-toc-text">信息及其度量</span></a></li><li class="post-toc-item post-toc-level-1"><a class="post-toc-link" href="#通信系统主要性能指标"><span class="post-toc-number">3.</span> <span class="post-toc-text">通信系统主要性能指标</span></a><ol class="post-toc-child"><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#有效性"><span class="post-toc-number">3.1.</span> <span class="post-toc-text">有效性</span></a></li><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#可靠性"><span class="post-toc-number">3.2.</span> <span class="post-toc-text">可靠性</span></a></li></ol></li></ol>
        </nav>
    </aside>


<article id="post-工作-wireless-2018-08-08-通信原理学习记录（一）"
  class="post-article article-type-post fade" itemprop="blogPost">

    <div class="post-card">
        <h1 class="post-card-title">通信原理学习记录（一）</h1>
        <div class="post-meta">
            <time class="post-time" title="2018-08-08 17:34:52" datetime="2018-08-08T09:34:52.000Z"  itemprop="datePublished">2018-08-08</time>

            
	<ul class="article-category-list"><li class="article-category-list-item"><a class="article-category-list-link" href="/categories/工作/">工作</a></li></ul>



            
<span id="busuanzi_container_page_pv" title="文章总阅读量" style='display:none'>
    <i class="icon icon-eye icon-pr"></i><span id="busuanzi_value_page_pv"></span>
</span>


        </div>
        <div class="post-content" id="post-content" itemprop="postContent">
            <h1 id="通信原理学习记录一">通信原理学习记录（一）</h1>
<p>今天刚刚开始学习通信原理，了解了通信原理的知识点，大概是要学习模拟通信与数字通信，模拟通信技术在之前的高频学习中已经有了一定的基础了，对一些调制技术有了一定的认识和分析能力，因此，本学习的通信原理主要的难度在于数字通信技术。</p>
<a id="more"></a>
<p>为了更好的学习通信原理，提前学习是个不错的选择，在<a href="http://www.icourse163.org/learn/NUDT-316006?tid=1002694004&amp;from=study#/learn/content" target="_blank" rel="noopener">MOOC上有个通信原理的课程</a>，阅读原文提供传送门。</p>
<figure class="image-bubble">
                <div class="img-lightbox">
                    <div class="overlay"></div>
                    <img src="/img/wireless/wireless_overview.png" alt="" title="">
                </div>
                <div class="image-caption"></div>
            </figure>
<p>一开始学习遇到了两个新的知识点：<strong>信息及其度量</strong>和<strong>通信系统主要性能指标</strong></p>
<h1 id="信息及其度量"><a href="#信息及其度量"></a>信息及其度量</h1>
<p>学过概率论的我们知道，事件的不确定程度可以用其出现的概率来描述。因此，消息中包含的信息量与消息发生的概率有关。消息出现的概率越小，蕴含的信息量越大。</p>
<p>使用<span class="math inline">\(P(x)\)</span>表示消息发生的概率，<span class="math inline">\(I\)</span>表示消息中的信息量</p>
<p><span class="math display">\[
I = log_a\frac{1}{P(x)} = -log_aP(x)
\]</span></p>
<p>通常使用单位为比特，公式可以简写为</p>
<p><span class="math display">\[
I = log_2\frac{1}{P(x)} = -log_2P(x)
\]</span></p>
<p>这种方法是使用算术平均的方法计算，还有另外一种是使用熵的概念计算</p>
<p><span class="math display">\[
H(x) = -\sum_{i=1}^M P(x_i) log_2 P(x_i)
\]</span></p>
<p>对于较多消息的信息量的计算选择熵的方式更好，因为使用熵的方式计算信息量更加准确，而且也更加方便。</p>
<p><strong>对信息度量的思考：</strong></p>
<p>我总感觉信息度量与密码学之间存在着联系，最简单的密码是通过查表实现的，比如将所有字母位置移1个位置，如A加1变换为B。</p>
<p>现在拥有一份这样加密的密文，统计发现其中某一个字母的出现次数最少，那么它拥有的信息量就最大，是不是就可以通过从这一个字母入手破解全篇的密文。</p>
<p>当然，这只是我的猜测而已，目前还并没有学习密码学的相关知识，在网上搜信息度量与密码学的关系也没搜出什么，估计也是我搜索的姿势不对。</p>
<h1 id="通信系统主要性能指标"><a href="#通信系统主要性能指标"></a>通信系统主要性能指标</h1>
<p>主要性能指标与<strong>有效性</strong>和<strong>可靠性</strong>有关</p>
<h2 id="有效性"><a href="#有效性"></a>有效性</h2>
<p>有效性的衡量与频带利用率有关</p>
<p>对于数字通信系统，频带利用率的定义为单位带宽内的传输速率</p>
<p><span class="math display">\[
\eta = \frac{R_B}{B} \ (Baud/Hz)
~~
or
~~
\eta_b = \frac{R_b}{B} \ (b/(s\cdot Hz))
\]</span></p>
<p>其中<span class="math inline">\(R_B\)</span>为码元传输速率，又称波特率。<span class="math inline">\(R_b\)</span>为信息传输速率，又称比特率。</p>
<p><em>ps: 突然看到波特率也是很兴奋的，学习串口通信那么久，终于看到了波特率的身影了；还有比特率也是好久以前听说的</em></p>
<p>码元速率与信息速率有以下关系</p>
<p><span class="math display">\[
R_b = R_B log_2 M \ (b/s)
\]</span></p>
<p>其中的M表示进制。例如，设码元速率为1200Baud，若采用八进制，则信息速率为3600b/s</p>
<p><em>ps:之前一直不知道MCU的串口通信中的波特率为什么越高，传输速度越快，现在终于知道了</em></p>
<h2 id="可靠性"><a href="#可靠性"></a>可靠性</h2>
<p>模拟通信系统的可靠性场用接收端输出信号与噪声功率比(S/N)来度量</p>
<p>数字通信系统的可靠性用差错概率来衡量。差错概率常用误码率和误信率表示。</p>
<p>误码率<span class="math inline">\(P_e\)</span>为错误码元数与传输总码元数之比</p>
<p>误信率<span class="math inline">\(P_b\)</span>为错误比特数与传输总比特数之比</p>
<hr>
<p>参考书籍：</p>
<ul>
<li>《通信原理》樊昌信第七版</li>
</ul>
<hr>
<figure class="image-bubble">
                <div class="img-lightbox">
                    <div class="overlay"></div>
                    <img src="/img/wechat_official_accounts.jpg" alt="" title="">
                </div>
                <div class="image-caption"></div>
            </figure>

        </div>

        <blockquote class="post-copyright">
    
    <div class="content">
        
<span class="post-time">
    最后更新时间：<time datetime="2018-09-09T05:52:39.288Z" itemprop="dateUpdated">2018-09-09 13:52:39</time>
</span><br>


        
        下方的留言框比较调皮，有时候故意不出来，而且还是滚刀肉，实在拿他没办法，所以如果等得不爽可以直接去<a href="https://github.com/greedyhao/greedyhao.github.io/issues" target="_blank" rel="external">issues</a>给我留言
        
    </div>
    
    <footer>
        <a href="http://greedyhao.cc">
            <img src="/img/portrait.jpg" alt="Greedyhao">
            Greedyhao
        </a>
    </footer>
</blockquote>

        
<div class="page-reward">
    <a id="rewardBtn" href="javascript:;" class="page-reward-btn waves-effect waves-circle waves-light">赏</a>
</div>



        <div class="post-footer">
            
	<ul class="article-tag-list"><li class="article-tag-list-item"><a class="article-tag-list-link" href="/tags/wireless/">wireless</a></li></ul>


            
<div class="page-share-wrap">
    

<div class="page-share" id="pageShare">
    <ul class="reset share-icons">
      <li>
        <a class="weibo share-sns" target="_blank" href="http://service.weibo.com/share/share.php?url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/&title=《通信原理学习记录（一）》 — Zhuhao's Blog&pic=http://greedyhao.cc/img/portrait.jpg" data-title="微博">
          <i class="icon icon-weibo"></i>
        </a>
      </li>
      <li>
        <a class="weixin share-sns wxFab" href="javascript:;" data-title="微信">
          <i class="icon icon-weixin"></i>
        </a>
      </li>
      <li>
        <a class="qq share-sns" target="_blank" href="http://connect.qq.com/widget/shareqq/index.html?url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/&title=《通信原理学习记录（一）》 — Zhuhao's Blog&source=通信原理学习记录（一）
今天刚刚开始学习通信原理，了解了通信原理的知识点，大概是要学习模拟通信与数字通信，模拟通信技术在之前的高频学习中已经有了一定的基础..." data-title=" QQ">
          <i class="icon icon-qq"></i>
        </a>
      </li>
      <li>
        <a class="facebook share-sns" target="_blank" href="https://www.facebook.com/sharer/sharer.php?u=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/" data-title=" Facebook">
          <i class="icon icon-facebook"></i>
        </a>
      </li>
      <li>
        <a class="twitter share-sns" target="_blank" href="https://twitter.com/intent/tweet?text=《通信原理学习记录（一）》 — Zhuhao's Blog&url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/&via=http://greedyhao.cc" data-title=" Twitter">
          <i class="icon icon-twitter"></i>
        </a>
      </li>
      <li>
        <a class="google share-sns" target="_blank" href="https://plus.google.com/share?url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/" data-title=" Google+">
          <i class="icon icon-google-plus"></i>
        </a>
      </li>
    </ul>
 </div>



    <a href="javascript:;" id="shareFab" class="page-share-fab waves-effect waves-circle">
        <i class="icon icon-share-alt icon-lg"></i>
    </a>
</div>



        </div>
    </div>

    
<nav class="post-nav flex-row flex-justify-between">
  
    <div class="waves-block waves-effect prev">
      <a href="/2018/08/11/工作-latex-2018-08-11-mathjax的基本操作/" id="post-prev" class="post-nav-link">
        <div class="tips"><i class="icon icon-angle-left icon-lg icon-pr"></i> Prev</div>
        <h4 class="title">mathjax的基本操作</h4>
      </a>
    </div>
  

  
    <div class="waves-block waves-effect next">
      <a href="/2018/07/31/工作-stm32-2018-07-31-LCD-TFT控制总结/" id="post-next" class="post-nav-link">
        <div class="tips">Next <i class="icon icon-angle-right icon-lg icon-pl"></i></div>
        <h4 class="title">LCD-TFT控制总结</h4>
      </a>
    </div>
  
</nav>



    


<section class="comments" id="comments">
    <div id="disqus_thread"></div>
    <script>
    var disqus_shortname = 'greedyhao';
    lazyScripts.push('//' + disqus_shortname + '.disqus.com/embed.js')
    </script>
    <noscript>Please enable JavaScript to view the <a href="https://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript>
</section>
















</article>

<div id="reward" class="page-modal reward-lay">
    <a class="close" href="javascript:;"><i class="icon icon-close"></i></a>
    <h3 class="reward-title">
        <i class="icon icon-quote-left"></i>
        谢谢打赏
        <i class="icon icon-quote-right"></i>
    </h3>
    <div class="reward-content">
        
        <div class="reward-code">
            <img id="rewardCode" src="/img/wechat.jpg" alt="打赏二维码">
        </div>
        
        <label class="reward-toggle">
            <input id="rewardToggle" type="checkbox" class="reward-toggle-check"
                data-wechat="/img/wechat.jpg" data-alipay="/img/alipay.jpg">
            <div class="reward-toggle-ctrol">
                <span class="reward-toggle-item wechat">微信</span>
                <span class="reward-toggle-label"></span>
                <span class="reward-toggle-item alipay">支付宝</span>
            </div>
        </label>
        
    </div>
</div>



</div>

        <footer class="footer">
    <div class="top">
        
<p>
    <span id="busuanzi_container_site_uv" style='display:none'>
        站点总访客数：<span id="busuanzi_value_site_uv"></span>
    </span>
    <span id="busuanzi_container_site_pv" style='display:none'>
        站点总访问量：<span id="busuanzi_value_site_pv"></span>
    </span>
</p>


        <p>
            
                <span><a href="/atom.xml" target="_blank" class="rss" title="rss"><i class="icon icon-lg icon-rss"></i></a></span>
            
            <span>博客内容遵循 <a rel="license" href="https://creativecommons.org/licenses/by-nc-sa/4.0/deed.zh">知识共享 署名 - 非商业性 - 相同方式共享 4.0 国际协议</a></span>
        </p>
    </div>
    <div class="bottom">
        <p><span>Greedyhao &copy; 2017 - 2018</span>
            <span>
                
                Power by <a href="http://hexo.io/" target="_blank">Hexo</a> Theme <a href="https://github.com/yscoder/hexo-theme-indigo" target="_blank">indigo</a>
            </span>
        </p>
    </div>
</footer>

    </main>
    <div class="mask" id="mask"></div>
<a href="javascript:;" id="gotop" class="waves-effect waves-circle waves-light"><span class="icon icon-lg icon-chevron-up"></span></a>



<div class="global-share" id="globalShare">
    <ul class="reset share-icons">
      <li>
        <a class="weibo share-sns" target="_blank" href="http://service.weibo.com/share/share.php?url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/&title=《通信原理学习记录（一）》 — Zhuhao's Blog&pic=http://greedyhao.cc/img/portrait.jpg" data-title="微博">
          <i class="icon icon-weibo"></i>
        </a>
      </li>
      <li>
        <a class="weixin share-sns wxFab" href="javascript:;" data-title="微信">
          <i class="icon icon-weixin"></i>
        </a>
      </li>
      <li>
        <a class="qq share-sns" target="_blank" href="http://connect.qq.com/widget/shareqq/index.html?url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/&title=《通信原理学习记录（一）》 — Zhuhao's Blog&source=通信原理学习记录（一）
今天刚刚开始学习通信原理，了解了通信原理的知识点，大概是要学习模拟通信与数字通信，模拟通信技术在之前的高频学习中已经有了一定的基础..." data-title=" QQ">
          <i class="icon icon-qq"></i>
        </a>
      </li>
      <li>
        <a class="facebook share-sns" target="_blank" href="https://www.facebook.com/sharer/sharer.php?u=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/" data-title=" Facebook">
          <i class="icon icon-facebook"></i>
        </a>
      </li>
      <li>
        <a class="twitter share-sns" target="_blank" href="https://twitter.com/intent/tweet?text=《通信原理学习记录（一）》 — Zhuhao's Blog&url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/&via=http://greedyhao.cc" data-title=" Twitter">
          <i class="icon icon-twitter"></i>
        </a>
      </li>
      <li>
        <a class="google share-sns" target="_blank" href="https://plus.google.com/share?url=http://greedyhao.cc/2018/08/08/工作-wireless-2018-08-08-通信原理学习记录（一）/" data-title=" Google+">
          <i class="icon icon-google-plus"></i>
        </a>
      </li>
    </ul>
 </div>


<div class="page-modal wx-share" id="wxShare">
    <a class="close" href="javascript:;"><i class="icon icon-close"></i></a>
    <p>扫一扫，分享到微信</p>
    <img src="" alt="微信分享二维码">
</div>




    <script src="//cdn.bootcss.com/node-waves/0.7.4/waves.min.js"></script>
<script>
var BLOG = { ROOT: '/', SHARE: true, REWARD: true };


</script>

<script src="//unpkg.com/hexo-theme-material-indigo@latest/js/main.min.js"></script>


<div class="search-panel" id="search-panel">
    <ul class="search-result" id="search-result"></ul>
</div>
<template id="search-tpl">
<li class="item">
    <a href="{path}" class="waves-block waves-effect">
        <div class="title ellipsis" title="{title}">{title}</div>
        <div class="flex-row flex-middle">
            <div class="tags ellipsis">
                {tags}
            </div>
            <time class="flex-col time">{date}</time>
        </div>
    </a>
</li>
</template>

<script src="//unpkg.com/hexo-theme-material-indigo@latest/js/search.min.js" async></script>



<!-- mathjax config similar to math.stackexchange -->

<script type="text/x-mathjax-config">
MathJax.Hub.Config({
    tex2jax: {
        inlineMath: [ ['$','$'], ["\\(","\\)"]  ],
        processEscapes: true,
        skipTags: ['script', 'noscript', 'style', 'textarea', 'pre', 'code']
    }
});

MathJax.Hub.Queue(function() {
    var all = MathJax.Hub.getAllJax(), i;
    for(i=0; i < all.length; i += 1) {
        all[i].SourceElement().parentNode.className += ' has-jax';
    }
});
</script>

<script async src="//cdn.bootcss.com/mathjax/2.7.0/MathJax.js?config=TeX-MML-AM_CHTML" async></script>




<script async src="//dn-lbstatics.qbox.me/busuanzi/2.3/busuanzi.pure.mini.js"></script>



<script>
(function() {
    var OriginTitile = document.title, titleTime;
    document.addEventListener('visibilitychange', function() {
        if (document.hidden) {
            document.title = '再见';
            clearTimeout(titleTime);
        } else {
            document.title = '你好';
            titleTime = setTimeout(function() {
                document.title = OriginTitile;
            },2000);
        }
    });
})();
</script>



</body>
</html>
